The present invention relates to integrated circuits and methods of operations thereof, and more particularly, to input buffer circuits and methods of operation thereof.
Integrated circuits often use input buffer circuits for receiving external signal and converting them to appropriate voltage levels. Input buffers preferably exhibit short delay time, small skew and low power consumption. Characteristic such as delay time may vary responsive to variation of power supply voltage applied to the input buffer circuit.
A typical input buffer circuit, as shown in FIG. 1, compares an input signal Vin to a predetermined reference voltage Vref. For example, the input buffer circuit 11 may include a differential amplifier that generates an output current that is proportional to the difference between the input signal Vin and the reference signal Vref, which is then used to produce a corresponding output signal Vout.
Referring to FIG. 2, when the difference Vsw between the input signal Vin and the reference voltage Vref is small, the output current may become so small that the slope of the curve describing the relationship between the input voltage difference Vsw and the output voltage Vout decreases. Consequently, the delay time and skew of the input buffer may increase. In addition, for small input voltage differentials, slowed transition of the output signal Vout may increase power consumption by circuits that receive the output signal Vout.
In embodiments of the present invention, an input buffer includes an amplifier circuit having an input terminal and an output terminal. A momentary boost circuit is coupled to an input buffer input terminal, the input terminal of the amplifier circuit, and the output terminal of the amplifier circuit, and is operative to generate a boosted input signal at the input terminal of the amplifier circuit from an input signal at an input buffer input terminal for an interval that is terminated responsive to an output signal at the output terminal of the amplifier circuit. The momentary boost circuit may include a detector circuit coupled to the output terminal of the amplifier circuit and operative to generate a control signal responsive to a transition of the output signal, and a boost circuit, coupled between the input buffer input terminal and the input terminal of the amplifier circuit and operatively associated with the detector circuit, that receives the input signal at the input buffer input terminal and generates the boosted input signal at the input terminal of the amplifier circuit from the received input signal responsive to the control signal. The boost circuit may include, for example, a capacitor coupled between the input buffer input terminal and the input terminal of the amplifier circuit, and a switch that couples and decouples the input terminal of the amplifier circuit to a reference voltage source responsive to the control signal. The detector circuit may be operative to generate a pulse responsive to a transition of the output signal, and the switch may be operative to couple the input terminal of the amplifier circuit to the reference voltage source responsive to the pulse.
In some embodiments of the present invention, the amplifier circuit includes a differential amplifier circuit having a first input terminal, a second input terminal, and an output terminal. The differential amplifier circuit is operative to generate an output signal at the output terminal responsive to a voltage between the first and second input terminals. The boost circuit is coupled between the input buffer input terminal and the first input terminal of the differential amplifier circuit, receives the input signal at the input buffer input terminal, and generates the boosted input signal at the first input terminal of the differential amplifier circuit from the received input signal responsive to the control signal.
In still other embodiments of the present invention, the amplifier circuit includes an inverting amplifier circuit. The boost circuit may include a capacitor coupled between the input buffer input terminal and an input terminal of the inverting amplifier circuit, and a switch that couples and decouples the input terminal of the inverting amplifier circuit to a reference voltage source responsive to the control signal.
In yet other embodiments of the present invention, the amplifier circuit includes a pull-up circuit that drives the output terminal responsive to a signal at a pull-up circuit input terminal, and a pull-down circuit that drives the output terminal responsive to a signal at a pull-down circuit input terminal. The boost circuit is coupled between the input buffer input terminal and the pull-up circuit and pull-down circuit input terminals, receives the input signal at the input buffer input terminal and generates the first and second boosted input signals at respective ones of the pull-up circuit and pull-down circuit input terminals from the received input signal responsive to the control signal. The boost circuit may include respective first and second capacitors that couple the input buffer input terminal to respective ones of the pull-up circuit input terminal and the pull-down circuit input terminal, and respective first and second switches that couple and decouple respective ones of the pull-up circuit input terminal and the pull-down circuit input terminal to a reference voltage node responsive to the control signal.
In method embodiments of the present invention, an input signal is received at an input buffer input terminal. A boosted input signal is generated at an input terminal of an amplifier circuit from the received input signal for an interval that is terminated responsive to an output signal produced at an output terminal of the amplifier circuit from the boosted input signal. A control signal may be generated responsive to the output signal, and the boosted input signal may be generated responsive to the control signal. In some embodiments of the present invention, the boosted input signal is generated by coupling a capacitor between the input buffer input terminal and the input terminal of the amplifier while decoupling the input terminal of the amplifier circuit and a reference voltage node responsive to a first state of the control signal, and then coupling the input terminal of the amplifier circuit to the reference voltage node responsive to a second state of the control signal to terminate generation of the boosted input signal.